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Old 2009-04-01, 23:36   #2
cheesehead's Avatar
"Richard B. Woods"
Aug 2002
Wisconsin USA

22·3·641 Posts

I'm not sure I'm the best qualified to make comprehensive specific recommendations for you, but here are a couple of responses about points I think I know:

(I presume others will correct me where I've grown rusty.)

Originally Posted by Discobadger View Post
(Love your nym, BTW.)

In the past I have just used Prime95 under torture test at standard settings using "In-place Large FFT's"
Normally the systems can run for 2 days quite easily without any errors.

However after speaking with a friend of mine he added that it will not be running a Complete system level test, it will only be torture testing the CPU.

Is this correct?
Not really. "In-place Large FFTs" also well-exercises the memory controller and bus, though it doesn't exercise as large a range of RAM addresses as Memtest does.

Should I be using small, blend or even a custom test?
They each have their strengths/weaknesses for the purpose of torture testing (that's why there are choices, of course :-), and a comprehensive testing scheme would use each of them in turn.

The small-FFT test exercises the CPU (especially the FPU) and L1 cache hard, but puts only a modest load on memory buses and RAM other than L1.

The large-FFT test exercises the CPU (especially the FPU) and L1/L2 cache hard (but possibly not as hard as small-FFT, if memory fetch is slow) and puts a heavy load on memory buses and non-cache RAM. However, the load it puts on main memory is not the same pattern as the load that Memtest puts on memory, so it is not a replacement for Memtest. Prime95 large-FFT is always fetching several megs of memory as fast as possible (thus stressing the memory controller and bus and cache), but is not systematically testing different parts of your RAM as Memtest does. (That's because the Prime95 torture test was not designed to be a general-purpose memory diagnostic test; it just turned out to be a good test in certain regards because the program optimizations are tuned to make maximum use of FPU and memory for purposes of fast FFT computation.)

The blend test steps through both small and large FFTs in a cycle, resulting in a combination of the small- and large-FFT tests.

The custom test is intended to allow specifying FFT size more particularly, in order to concentrate testing on a suspected critical size or range of sizes.

Even though the system is running at 100% load the system is still pretty responsive, which is whats leading me to the assumption that I've not got prime setup & torture testing to the best of its abilities.
(1) Hey! Prime95's purpose is not to bring your system to its knees! Its purpose is to maximize throughput of certain mathematical computations (which might happen to inspire kneebends on some marginal systems, but that isn't the direct intent) while affecting responsiveness as little as possible.

Prime95 is not some random video game! It's serious (but not too-serious ; maybe sincere is more accurate) sincere software, carefully tuned over several years.

(2) Prime95 is specifically designed to interfere as little as possible with other tasks running on your system. It does this by running all of its computation-intensive code at the lowest system priority, so that any other task your system is doing can easily interrupt that part of the code when necessarily. So you can see 100% CPU, but you don't see that it's 99% at lowest priority and only 1% at higher priorities. That way, your system remains responsive to non-Prime95 tasks. We're trying to be modest and unassuming while conducting blazing-fast calculations on enormously large numbers!!!

Having said that ... when the large-FFTs are running, there may be a greater chance that other system tasks using large amounts of RAM will encounter higher swapping/paging rates than they would if prime95 were not running, because of somewhat increased competition for real memory space. Prime95's low priority will mean its pages will be the ones selected to page/swap out, but that does take a bit of time, plus the extra time to read in pages for the other tasks.

Regarding "options>cpu settings and information" Should I have a maximum memory amount set here?
Only if you'll do a lot of P-1 or ECM work. It's not documented well, but "available memory" matters _only_ during P-1 stage 2 and ECM stage 2. At all other times, such as during LL, DC or TF, it is ignored and doesn't matter.

Last fiddled with by cheesehead on 2009-04-01 at 23:57
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